Research On Energy Management Method Of Vehicle Hybrid Energy Storage System

Consumer concerns about driving range,charging time and battery life remain key factors limiting the development of electric vehicles.Energy storage devices represented by Lithium-ion batteries have high energy density and low self-discharge effect,which are widely used in electric vehicle energy storage systems.However,a single energy storage device cannot meet the requirements of high energy density and high power density of electric vehicles.Ultra-capacitor is added to form a hybrid energy storage system,which can realize complementary advantages by virtue of its high power density and high cycle life.Therefore,based on a full understanding of the respective characteristics of two different energy storage devices,research on the topology structure and energy management strategies of hybrid energy storage systems is carried out for the overall economic cost,service life,and other goals of hybrid energy storage systems.It is of great significance to alleviate the impact of harsh working conditions on the life of Lithium-ion batteries,improve their utilization level.The main contents of this paper are as follows:(1)Focused on the problems such as the influence of high frequency power demand on battery life of electric vehicles,a closed-loop Haar wavelet transform energy management strategy was proposed based on the analysis of the basic principle of Haar wavelet transform.The high frequency component and the low frequency component of the power demand are separated through Haar wavelet transform to reduce the impact of high frequency power demand on the life of Lithium-ion batteries.Two closed-loop strategies,nonlinear proportional algorithm and PI controller,are used to dynamically adjust the output current of the Lithium-ion battery to maintain the stability of the DC bus voltage.Finally,the experiment is carried out under the simulation of Chinese passenger car operating conditions.The experimental results show that the proposed two closed-loop Haar wavelet transform energy management methods can control the maximum voltage deviation of the DC bus within 2.75% and 1.28% respectively.It can not only maintain the bus voltage stability,but also effectively reduce the influence of high frequency power demand on the life of Lithium-ion battery,and reduce the surge current sustained by Lithium-ion battery.(2)In order to reduce the system loss and reduce the problem that the DC bus voltage fluctuates greatly with the ultra-capacitor voltage in semi-active topology.Firstly,the Lithium-ion battery model and DC/DC converter efficiency model are established.On this basis,the multi-objective cost function is constructed to reduce the power loss of the energy storage system and stabilize the DC bus voltage,and the optimal solution is obtained by Differential Evolution algorithm.Finally,the experimental verification is carried out in the simulation of China light-duty vehicle test cycle for passenger car.Experimental results show that the proposed hybrid energy storage system energy management method can control the maximum busbar voltage deviation within 1.23%,and the system efficiency reaches 85.27%.(3)Based on the constructed Lithium-ion battery model,DC/DC converter efficiency model and cost function,the energy management method of hybrid energy storage system based on Particle Swarm Optimization was proposed.Then the optimal solution is found in the solution space by particle swarm optimization algorithm.Finally,experimental verification is carried out under simulated highway fuel economy test.Experimental results show that the voltage overshoot of the DC bus is only 0.5%,and the system efficiency reaches91.79%.